Generally, a thermoplastic polyester, for example, polyethylene terephthalate, has excellent mechanical properties, and is broadly used for a formed product of a film, a fiber, etc.
Usually, in the polyester, inert particles are contained in the polyester and thereby form protrusions on the back surface of a formed product for the purpose of giving a slipping property to the formed product. Although there are various kinds of particles as such inert particles, there is a problem that generally inert particles are poor in affinity with polyester and in abrasion resistance.
To solve this problem, investigations with respect to surface treatment have been carried out. For example, JP-A-SHO 63-221158 and JP-A-SHO 63-280763 propose to improve the surfaces of colloidal silica particles by a glycol group, JP-A-SHO 63-312345 proposes to improve the surfaces of colloidal silica particles by a coupling agent, and JP-A-SHO 62-235353 proposes a surface treatment of calcium carbonate particles by a phosphorus compound.
However, even if such conventional methods are applied, in a case of use with a contact running and friction such as a magnetic tape, particles are likely to fall off. Therefore, use of particular particles is recently proposed. Specifically, it is proposed that aluminum oxide particles have a great advantage for increase of abrasion resistance, for example, in JP-A-HEI 2-129230 (delta-type aluminum oxide particles) and in JP-A-HEI 2-38444 (aluminum oxide particles).
However, even if such methods are applied, when a film is brought into contact with a guide pin and repeatedly runs at a high speed, the abrasion resistance and the scratch resistance thereof are insufficient.
The inventors of the present invention have found that the abrasion resistance and scratch resistance of a polyester film depend upon the kind of particles present in the polyester film, and have reached the present invention as the result of earnest investigation.
An object of the present invention is to solve the above-mentioned disadvantages in the conventional technologies, and to provide a thermoplastic polyester composition excellent in all of slipping property, abrasion resistance and scratch resistance, particularly a thermoplastic polyester composition from which films and fibers excellent in abrasion resistance in repeated high-speed running can be made.